The present invention relates to an internal combustion engine mounted on a small planing watercraft, and more particularly to a four-cycle internal combustion engine with a dry sump lubricating system with an improved engine oil tank for a small planing watercraft.
A small planing watercraft for running on a water surface by ejecting water rearward by a water jet pump mounted on a rearward bottom portion of a hull is a watercraft with a high sports utility, and therefore a two-cycle engine small in size and light in weight normally is mounted thereon. A two-cycle engine which accumulates no engine oil in the crank case has the advantage that no engine oil flows into the combustion chamber in case the small planing watercraft turns over. A two-cycle engine, therefore, is suitable for a small planing watercraft.
In recent years, a four-cycle engine with relatively low noise level and clean exhaust gasses has been examined for mounting on a small planing watercraft in view of the need of environmental protection. Attempts have been made to employ a dry sump lubrication system in which no engine oil is accumulated in the crank case, for preventing the engine oil from flowing into the combustion chamber from the crankcase even when the small planing watercraft turns over.
A small planing watercraft having mounted thereon a four-cycle internal combustion engine with a dry sump lubrication system is disclosed in JP-A-7-237586 and JP-A-7-237587. In a small watercraft disclosed in the former publication, an engine oil tank is arranged under an air suction device and communicates through an oil pump with an oil pan arranged under the engine. In a small watercraft of the latter publication, on the other hand, an oil tank for engine lubrication is arranged above a coupling between an engine output shaft extending in the longitudinal direction of the watercraft and an impeller shaft, and communicates through the oil pump with the oil pan arranged under the engine.
In all the above-mentioned engines, however, the oil tank is separately mounted from the engine body, and therefore a space and parts are required for mounting the oil tank. Also, external pipings are required for transporting the oil from the crankcase to the oil tank by means of a scavenging pump, and for supplying the oil from the oil tank to various parts of the engine by means of a feed pump. Consequently, the mounting space and the weight of the engine including the oil tank are increased. Further, the external pipings are complicated and increase the mechanical loss due to the flow resistance in the pipings, leading to the problem of a delayed response to an oil pressure increase. Furthermore, in the case where the oil tank is arranged to communicate with a suction device of the engine to send a blow-by gas in the oil tank through a breather pipe to the air suction device, the engine oil in the oil tank tends to flow out through the breather pipe when the small planing watercraft turns over.
The present invention has been developed in view of the above-mentioned problems which have been posed when a four-cycle engine with a dry sump lubrication system is mounted on a small planing watercraft.
Accordingly, an object of the invention is to provide a compact, lightweight, and rigidity increased four-cycle engine with dry sump lubrication system mounted on a small planing watercraft.
Another object of the invention is to provide a four cycle engine with a dry sump lubrication system for a small planing watercraft, in which the mechanical loss due to the flow resistance in the piping is reduced for an improved oil-pressure rise response, and the mounting space of the engine is reduced by simplifying the oil piping system.
Still another object of the invention is to provide a four cycle engine with a dry sump lubrication system for a small planing watercraft, in which the engine oil is prevented from flowing into a combustion chamber while at the same time preventing the engine oil from flowing out of an oil tank when the small planing watercraft turns over.
A further object of the invention is to provide a four cycle engine with a dry sump lubrication system for a small planing watercraft, in which the separability of the engine oil from the blow-by gas in the oil tank is improved and the oil is prevented from flowing out of a breather passage along with the blow-by gas.